This application is a continuation application Ser. No. 10/800,752, filed Mar. 16, 2004 now U.S. Pat. No. 6,949,856 which is a continuation of Ser. No. 10/142,154, filed May 10, 2002 (now U.S. Pat. No. 6,734,592), which is a continuation of Ser. No. 10/142,220, filed May 10, 2002 (now abandoned), which is a continuation of Ser. No. 09/488,637, filed Jan. 21, 2000 (now U.S. Pat. No. 6,396,183), which is a continuation of Ser. No. 08/838,745, filed Apr. 11, 1997 (now U.S. Pat. No. 6,034,460), and claims priority of Japanese patent document JP8-091014, filed Aug. 12, 1996.